Strategy for Ensuring the Metrological Traceability of Nanoparticle Size Measurements by SEM

The concept of measurement traceability is crucial for ensuring the data reliability and the comparability of measurement results provided by different instruments and operators. In the field of nanoparticle metrology, determining the size of nanoparticles using electron microscopy-based techniques remains a real challenge. In laboratory settings, the establishment of traceability regarding the instrument calibration procedures, the assessment of uncertainties associated with instruments/operators/samples/environments, as well as the complexities related to electron-sample interactions, are often neglected. In this article, we describe the calibration procedure set up at the LNE (Laboratoire National de métrologie et d'Essais) and propose an evaluation method for determining the uncertainties in measuring nanoparticle size by SEM (Scanning Electron Microscopy). This study investigates the impact of the energy of the primary electrons (PEs) generated by the electron beam and accelerating voltage on the reliability of size measurements. The convolution between the signals coming from a nanoparticle and the substrate on which the particle is deposited induces edge effects that can have a negative impact on the measurement results. Finally, a diagram describing the various stages involved in establishing traceability for SEM measurements of nanoparticle size is proposed to facilitate the work of future operators.